1. Field of the Invention
The present invention relates to an inclined angle adjusting mechanism and an inclined angle adjusting method for finely adjusting the angle of rotary shaft of a disk motor with respect to the optical axis of an optical pickup in a disk device for recording or reproducing information on an optical disk.
2. Description of the Related Art
In general, in a disk device, a disk motor base is placed on a mechanical chassis side base (hereinafter referred to as a mechanical chassis base). To this disk motor base are fixed a turntable having an optical disk placed thereon and a disk motor for rotating this turntable. The respective rotary shafts of the disk motor and the turntable are set so as to be perpendicular to the disk motor base. Moreover, on the mechanical chassis base is arranged an optical pickup movable in a radial direction of the optical disk placed on the above mentioned turntable. Laser light of the optical pickup needs to be adjusted in such a way as to be substantially at right angle with respect to the optical disk in order to record or reproduce information on the optical disk. For this purpose, for example, as disclosed in Japanese Unexamined Patent Publication No. 2000-99974, between the mechanical chassis base and the disk motor base is arranged an inclined angle adjusting mechanism by which the angle of rotary shaft of the disk motor with respect to the optical axis of the optical pickup arranged on the mechanical chassis base is finely adjusted by finely adjusting an angle at which the disk motor base is mounted on the mechanical chassis base.
FIG. 17 is a cross sectional view to show the structure of an inclined angle adjusting mechanism in a disk device in the prior art disclosed in the above mentioned official patent gazette. In the drawing, a reference symbol 1 denotes an optical disk, 2 denotes a turntable on which the optical disk 1 is placed, 3 denotes a spindle motor (hereinafter referred to as a disk motor) for rotating the turntable 2, 3a denotes an output shaft of the disk motor 3, and 4 denotes a mechanical chassis base. In the mechanical chassis base 4 is made a circular opening 4a and in a peripheral edge portion of this opening portion 4a are formed three screw holes (in FIG. 17, only screw holes 4b and 4c are shown). On the other hand, disk motor 3 is fixed to the disk motor base 5, over its central hole 5a, and in the peripheral edge portion of this disk motor base 5 are formed three screw holes (in FIG. 17, only screw holes 5b and 5c are shown). The disk motor base 5 is fixed, for example, by screwing the screws 6b and 6c into the peripheral edge portion of the opening 4a of the mechanical chassis base 4. A spacer 7 is arranged between the mechanical chassis base 4 and the disk motor base 5 at an outer peripheral portion of the screw 6c. Moreover, a compression spring 8 as an urging spring is arranged between the mechanical chassis base 4 and the disk motor base 5 at the outer peripheral portion of the screw 6b. Here, the screw 6b and the compression spring 8 constitute an inclined angle adjusting mechanism in the prior art.
Next, an operation will be described.
By screwing in the screw 6c, a difference in height between the disk motor base 5 on the screw 6c side and the mechanical chassis base 4 is set by the thickness of the spacer 7. Next, a difference in height between the disk motor base 5 on the screw 6b side and the mechanical chassis base 4 is adjusted against the urging force of the compression spring 8 by screwing in the screw 6b. In this manner, an angle θ between the output shaft 3a of the disk motor 3 and the mechanical chassis base 4 is finely adjusted near substantially at 90 degrees.
However, since the inclined angle adjusting mechanism in the prior art has the above mentioned structure, it has the following problem.
In general, it is preferable that an urging spring in the inclined angle adjusting mechanism has such a low spring constant in a range of adjusting stroke as to vary an urging force as little as possible, but at the same time, it is also required that the urging spring has a holding force which is high enough to hold an inclined angle against vibrations and an impact force caused by the disk motor 3 after adjusting the inclined angle. For this reason, in a case where the urging spring is constituted by the compression spring as shown in FIG. 17, it is necessary to use the compression spring producing a strong urging force to give priority to holding the inclined angle after adjustment. In this case, it is difficult to perform an adjusting work. Moreover, in a case where the compression spring satisfying this required specification is used, it is necessary to provide a space in which the compression spring is arranged in the direction that adjusts height (product thickness), so that it is impossible to make a product thinner.
In contrast, there has been also known the inclined angle adjusting mechanism in which the urging spring is constituted by a leaf spring in place of the compression spring. In this case, there is presented the following first problem: although it is possible to become the product thinner by a use of the leaf spring, in order to satisfy the above mentioned specification, inevitably, its plan size is made larger and thus the whole mechanism is made larger in size, and in particular, an integrated type leaf spring integrally formed by a plurality of spring pieces can not satisfy the above mentioned required specification because in an integrated type leaf spring it is impossible to make only a spring piece which is made slender to avoid interfering with the other parts, of a material having a high spring force.
Further, there is presented the second problem that when parts such as disk motor base and the like are assembled, it is necessary to position parts against the leaf spring having a high urging force (reactive force) satisfying the above mentioned required specification and to fix them with screws, which results in making the assembling work and the following adjusting work troublesome.
Still further, there is presented the following third problem: when the disk motor base is positioned in the direction of plane of the mechanical chassis base before adjusting the inclined angle, when a cylindrical reference component provided on the mechanical chassis base is fitted in a circular hole made in the disk motor base, because the outer diameter of the reference component and the inside size of the circular hole vary within part tolerances, the gap between both of them varies; and this makes positioning unstable, and in particular, when a shift in position in the direction of the disk motor base which is related to a disk jitter becomes considerably large, it degrades reproducing characteristics.
Still further, there is presented the following fourth problem: in the inclined angle adjusting method using the adjusting screws and the leaf spring, the screws are loosened in some cases with the elapse of time after adjustment by vibrations and temperature changes to impair the adjustment; and as a countermeasure against this, it is thought to fix the screws with an adhesive after the adjustment, but since there is a case where parts of the disk motor base need to be replaced in some cases after they are fixed, the parts can not be completely fixed with the adhesive.